Mass cytometry is a novel technology that merges aspects of flow cytometry with mass spectrometry, thereby enabling studies that would not be feasible with either technology alone. This approach utilizes elemental mass antibody tags, rather than fluorophores, and as each elemental mass channel is distinct, no signal compensation is required. Importantly, the single cell resolution of flow cytometry is retained, thus permitting the delineation of complex cell subsets within primary blood or bone marrow samples. Presently, ~32 parameters can be measured simultaneously with this technology, and with further development, up to 50-100 markers is likely. This approach requires the use of a specialized instrument (CyTOF) designed specifically for this analysis. There are currently no similar instruments available at Washington University or the surrounding vicinity. Acquisition of a CyTOF will enable at least 13 NIH-funded investigators at Washington University to conduct studies that will transform the fields of hematopoietic development, stem cell biology, and tumor immunology.